ES2290049T3 - PRODUCTION METHOD FOR THERMOPLASTIC RESIN FOAM AND MOLDING MOLD FOR THE SAME. - Google Patents

Abstract

Procedure for producing a foamed body of a thermoplastic resin by pouring the molten thermoplastic resin and containing a foaming agent into a cavity of a mold and then expanding the cavity to expand the resin, including the procedure the steps of: keeping the cavity in its shape filled with the resin for a predetermined period of time after the resin containing the foaming agent is completely poured into the cavity, and extending the cavity to an increased final cavity width after the predetermined period of time, characterized in that the cavity to an increased final cavity width after the average temperature of the molten resin within the cavity reaches the range of the melting point of the resin to [melting point + 30 ° C].

Description

Production method for resin foam thermoplastic and molding mold for it.

The present invention relates to a procedure to produce resin foamed bodies thermoplastic filling the cavity of a mold with the resin thermoplastic molten and containing a foaming agent, and expanding  then the cavity, and to molds for use in the procedure to produce the foamed resin body.

As already described, for example, in the JP-B publication no. 51-8424 (1976), a procedure is known to produce a thermoplastic resin foamed body filling the cavity of a mold with molten thermoplastic resin and containing a foaming agent, and then expanding the cavity. As shown in Figure 12 on a line 91, the cavity is extended in this procedure at a speed of V2 for a period of time T2 after the end of the fill.

A procedure is also known in which the cavity is enlarged at different speeds to get a body Foamed that has a desired touch feel, controlling the thickness of an unexpanded skin layer, as described, by example, in JP-A publication no. 7-88878 (1995). With this procedure, the cavity is enlarged at a speed of V1 so far T1 after completion of filling and then at a lower speed V3 from moment T1 to moment T2.

JP-B Publications No. 51-8424 (1976) and JP-A nº 6-198668 (1994) describe a procedure in which the cavity of a mold used is enlarged to form a Foamed body of thermoplastic resin. This procedure prepares an expanded molded part filling the cavity with the resin thermoplastic molten and containing a foaming agent, and forcing then the cavity to expand it quickly by an amount default

The foamed body is produced by this procedure loading the thermoplastic resin containing a foaming agent in the cavity kept diminished with respect to the final form of it and subsequently extending the cavity to final product size.

However, conventional procedures to produce thermoplastic resin foamed bodies have the problem that it is difficult to get large foamed bodies expansion ratio, for example those that have properties thermal insulators and an expansion ratio of at least 5 times. Other problem encountered is that the conventional procedure provides only those with a cell diameter as large as  at least several millimeters, producing only molded parts hollow in case of inadequate conditions.

Additionally, the procedures Conventionals have the problem that the resin stops expand completely in the corners of the cavity of compliance with the cavity enlargement. Said more specifically, when a resin 104 containing an agent Foaming agent is loaded into a cavity 103 defined by a fixed mold 101  and a movable mold 102, as shown in Figure 13 (a), and when the cavity 103 is expanded then moving the mold mobile 102 towards the direction of arrow 107, as shown in the Figure 13 (b), thermoplastic resin 104 is likely stop expanding at the corners of the cavity 103 in accordance with the enlargement of the cavity 103, providing accordingly only a foam body 106 that is lowered in the corners 105.

On the other hand, the publication JP-A No. 10-230528 (1998) describes a procedure to produce a foamed body that it has a superficial layer of the entire unexpanded portion with the same and of satisfactory surface appearance and that has thin closed cells with a uniform average cell density, using carbon dioxide or nitrogen in a supercritical state as a foaming agent.

JP-A publication no. 8-108440 (1996) describes an expanded board of polyolefin resin having a cell structure closed, (a) at least 85% of which are 2.5 to 10.0 in the ratio of their size in a direction perpendicular to board plane to the size of them in a parallel direction to the board, and (b) at least 70% of which are up to 500 \ mum in a direction parallel to the board plane, the board being expanded by at least 2 in relation to the compressive strength thereof in one direction perpendicular to the plane of the board to compressive strength thereof in a direction parallel to the plane of the board, and 5 to 20 times in the expansion ratio. This expanded board of polyolefin resin is produced from a resin mixture of polyolefin, a chemical foaming agent and a crosslinking agent applying pressure to the mixture, using molds that have opposite parallel interior surfaces, heating the mixture to a temperature not lower than the decomposition temperature of the foaming agent and subsequently increasing the distance between the molds to expand the polyolefin resin only in a direction perpendicular to the interior surfaces to through which the pressure is applied. This procedure It involves ingenuity to produce a flattened cell structure with in order to achieve a low density and high rigidity at compression.

However, since the procedure of JP-A production no. 10-230528 (1998) is a molding procedure  by injection, the foam body obtained is low in resistance to compression and properties to absorb large impacts due to its thin and uniform closed cell structure, although It has form adaptability. Therefore, the product needs to higher density is provided in order to improve your physical properties, while this entails the problem of make the molded part heavier and not damaged in thermal insulating properties.

The molded part of JP-A nº 8-108440 (1996) consists only of one layer expanded that provides a monolayer structure and therefore is low in flexural strength and small in the limit of deformation due to the presence of closed cells. Therefore the procedure, as described above, has the problem of providing molded parts only in the form of board. The use of the chemical foaming agent results in a increased cost and allows unreacted components and decomposed agent products remain in the body foaming, which results in body discoloration foaming, odor release and hygiene problems food

The document EP-A-0 839 624 describes a procedure for the production of the foamed body. At procedure, molten thermoplastic resin, containing A sparkler is loaded into a cavity of a mold. The cavity of mold containing the thermoplastic resin is kept in the state filling for a predetermined period of time and, to then the cavity is extended to a cavity width final.

The document US-A-5,547,621 also describes a procedure for the production of a foam body. A resin molten thermoplastic comprising a foaming agent is loaded into A cavity of a mold. The cavity is maintained in the state of filled for a predetermined time and then it extends to a final cavity width. In addition, a useful mold in the procedure. The mold comprises a member stationary and a moving member that define a cavity. Within the cavity is arranged a moving part that can move towards forward or backward along the thickness direction. The moving part is shaped such that it defines a space of peripheral cavity and a main cavity space. The space of peripheral cavity is defined by the immovable piece, a outer peripheral surface of the moving part and a wall of peripheral cavity The main cavity space is defined by a front end face of the moving part and a wall of Cavity opposite it.

An object of the present invention is to improve the procedure of the aforementioned class and the mold of the class mentioned above.

This object is resolved by the procedure of claim 1 and the mold of claim 7.

The invention provides as a feature additional thereof a procedure to produce a body foaming of a thermoplastic resin that is characterized by expanding the cavity at the width of the final cavity increased by one speed of 2 to 5 mm / s.

The invention provides as a sixth characteristic of it a procedure to produce a body foaming of a thermoplastic resin according to the second, fourth or fifth features of the invention, the procedure being characterized by extending the cavity to a speed of 5 to 10 mm / s in the secondary expansion step of the cavity.

The invention provides as seventh characteristic of it a procedure to produce a body foaming of a thermoplastic resin according to any one of the first to sixth features of the invention, the procedure being characterized because the foaming agent is a inert gas, namely a gas that is not reactive with the resin.

The term "direction of movement towards front ", as used here, refers to the address in the that the moving part moves towards a drinking fountain portion of the cavity in order to decrease the cavity and therefore to the direction indicated in 51 in figure 4 (b). The term "address of backward movement "refers to the direction in which the moving part moves away from the trough portion of the cavity to extend it and, consequently, to the indicated direction at 52 in Figure 4 (b).

The invention provides as an eighth characteristic of it a mold to form a foamed body of a thermoplastic resin according to the method of any of claims 1 to 6, which has a cavity defined by a stationary mold member and a movable mold member that it is provided with a moving part that can move forward or backward along the thickness direction of the cavity 31, the moving part being shaped so that it defines a space 32 of peripheral cavity by means of a peripheral surface exterior of the moving part and a wall 33 of peripheral cavity, and a space 34 of main cavity by means of an extreme face front of the moving part and a wall 35 of opposite cavity to the same when the moving part moves forward.

The width t4 of the cavity space 32 peripheral is two to four times the width t3 of space 34 of main cavity

With reference to Figure 4 (a), the width t4 of the peripheral cavity space 32 is 2 to 4 times, preferably 2.7 to 3.5 times the width t3 of space 34 of main cavity

If the width t4 of the cavity space 32 peripheral is less than twice the width t3 of space 34 of main cavity, the peripheral portion of the resin body foam thermoplastic that you want to obtain stops adapting to the mold shape, and it is likely that a body will not be available Foamed as desired. If the width t4 of space 32 of peripheral cavity is greater than four times the width t3 of the Main cavity space 34, the resin foamed body thermoplastic will deform when it cools insufficiently, ceasing to have the desired shape. It is likely that an attempt to cooling the body sufficiently leads to productivity widely reduced It is also likely that the resin thermoplastic within the peripheral cavity space 32 is not expand to its full extent.

The peripheral cavity space 32 may have the shape of an integral tube and can be rectangular parallelepiped or of another polygonal or circular configuration in section cross.

With reference to Figure 4 (a), a moving part 221a arranged in a movable mold member 22a shape a tubular cavity 31 having a bottom and, for example, a lowered section along the direction of movement towards Forward or backward when moving forward in maximum degree. The bottom tubular cavity 31 comprises a cavity space 32 peripheral defined by the outer peripheral surface of the moving part 221a and a peripheral surface 33 of cavity, and a main cavity space 34 defined by the extreme face front of the moving part 221a and a wall of cavity 35 opposite to the same.

The invention provides as a ninth characteristic of it a mold to form a foamed body of a thermoplastic resin according to the eighth characteristic of the invention, the mold being characterized in that the length t5 of the peripheral cavity space 32 in the direction of movement towards front or back is greater than the width t3 of space 34 of main cavity in the direction of forward movement or backward.

With reference to Figure 4 (a), it is desired that the length t5, along the direction of movement towards front or back of the peripheral cavity space 32 of the tubular cavity 31 having a bottom and, for example, a section reduced, be greater than the width t3 of the cavity space 34 principal.

The invention provides as a tenth characteristic of it a mold to form a foamed body of a thermoplastic resin according to the eighth or ninth characteristic of the invention, the mold being characterized in that the length t5 of the peripheral cavity space 32 in the direction of movement forward or backward is 50 to 70% of a width t6 of final cavity increased.

With reference to Figure 4 (a), the t5 length, along the direction of forward movement or backward, from the peripheral cavity space 32 of the cavity tubular 31 having a bottom and, for example, a recessed section, it is preferably 50 to 70%, more preferably 60 to 65%, of t6 width of final cavity increased.

If the length t5 is less than 50% of the width t6 of the increased final cavity, the resin foamed body thermoplastic obtained has a peripheral portion that stops adapt to the shape of the mold. It is likely then that it is not available the product in the desired way. If the length t5 is greater than 70% of the width t6 of the increased final cavity, is likely that the thermoplastic resin foamed body obtained have wrinkles and a damaged appearance.

The thermoplastic resin to be used in the The present invention is not specifically limited. Examples of Useful resins are polyethylene, polypropylene, copolymer of ethylene-propylene copolymer of ethylene-propylene-diene, copolymer ethylene vinyl acetate, polybutene, chlorinated polyethylene and similar olefin resins, polystyrene, copolymer of styrene-butadiene-styrene, resin of styrene-isoprene-styrene, methyl polyacrylate, copolymer of ethylene-ethyl acrylate and acrylic resins similar, polyvinyl chloride and similar chlorine resins, polyethylene fluoride and similar fluorocarbon resins, 6-nylon, 66-nylon, 12-nylon and similar polyamide resins, polyethylene terephthalate, polybutylene terephthalate and resins of Similar polyester, ABS resin, polycarbonate, polyacetal, sulfide polyphenylene, polyether ether ketone, polyetherimide, resin silicone, thermoplastic urethane, various elastomers, etc.

Among these examples are especially preferable resins that have a melt stress or a Stretch viscosity suitable for expansion. Such favorably useful resins are, for example, polyethylene, polypropylene, polystyrene, ABS resin, polyvinyl chloride, etc. Examples of useful polyethylene and polypropylene are resins finely crosslinked that fit in its characteristics of stretch viscosity

These resins can be used individually or at least two of them can be used in the form of an alloy, mixture or composite material.

The term "melting point" is defined as the temperature at which a resin changes from a fluid state to a non-fluid state In the case of crystalline resins, such as polyethylene, polypropylene, polyacetal, terephthalate Polybutylene, melting temperature Tpm, measured according to JIS K7121, is used as the melting point. In the case of non-crystalline resins, such as polystyrene, polyacetate vinyl, methyl polymethacrylate, polycarbonate and ABS resin, the glass transition temperature Tmg, measured according to JIS K7121, is taken as a melting point. Although vinyl chloride is a crystalline resin, the thermal decomposition temperature of it approximates the melting temperature Tpm thereof and The resin is molded at a temperature up to the temperature of Tpm fusion. In the case of crystalline resins that are molded to a temperature not higher than the melting temperature Tpm, [the melting temperature Tpm-30 ° C] is taken as the melting point. Similarly, with non-crystalline resins that are molded to a temperature up to the glass transition temperature Tmg, [the glass transition temperature Tmg - 30 ° C] is taken as the point of fusion.

The term "average temperature of the resin ", as used herein, is defined as the average value of the temperature of the resin layer poured into the mold cavity in the direction of the thickness of the layer. Although the temperature in the Thickness direction of the resin layer is not limited particularly, the temperature is preferably the value in the middle portion of the trough portion of the mold and the end front of the resin layer, that is, in the middle portion of the layer thickness

The temperature of the molten resin and filling the mold is determined, for example, by measuring the temperature of the resin layer loaded with an infrared temperature sensor installed in the mold or calculating the temperature of the layer of resin loaded by flow analysis by CAE injection.

The expressions "cavity maintenance fills "e" interruption of the cavity enlargement ", as  they are used here, they mean the state of the moving part substantially in a detention position, and refer to state in which the speed of enlargement by the moving part is of up to 0.1 mm / s. However, the speed of expansion by the Moving part is preferably 0 mm / s.

The foaming agent for use herein invention is not particularly limited, but agents are useful thermally organic or inorganic chemical foaming agents decomposibles or physical foaming agents. Examples of agents Useful chemical foaming agents are azo compounds, composed of hydrazide, nitrous compounds, semicarbazide compounds, Hydrazo compounds, tetrazole compounds, ester compounds, bicarbonates, carbonates, nitrites, etc. More specific examples they are azodicarbonamide (ADCA), isobutyronitrile (AZDN), benzenesulfonylhydrazo (OBSH), dinitropentamethylenetetramine (DPT), azobisisobutyronitrile (AIBN), p-toluenesulfonhydrazide (TSH), azodicarboxylate barium (Ba-Ac), etc. Examples of foaming agents physicists are carbon dioxide gas, argon, neon, helium, oxygen and similar non-reactive gases. These agents can be used individually or at least two of them are usable in combination.

The method of expanding the mold cavity does not It is particularly limited. For example, the moving part of the mold moves towards a direction by means of a mechanism hydraulic for an injection molding machine, as shown in figures 2 and 3, or an external hydraulic device and a hydraulic piston to extend the cavity, or the cavity is wide using a mold opening mechanism for a machine injection molding, as shown in figures 5 and 6.

The "cavity width resulting from the passage of primary enlargement of the cavity "according to the characteristics second, fourth or fifth of the invention is not limited particularly if the width is not greater than the width 16 of final cavity increased. However, the width is preferably up to 3.0 times the width t3 of space 34 of main cavity in the direction of forward movement or backwards, more preferably up to 6.5 mm. If the width increased by primary enlargement is excessively large, it is the cell film is likely to break, joining large amounts of small cells to form large cells.

The "primary expansion step speed of the cavity "according to the invention and the" speed of the enlargement to the final cavity width "are preferably of 0.5 to 15 mm / s, more preferably 2 to 5 mm / s. If the speed Cavity enlargement is too low, you only get a foamed body of large cells. If the speed is excessively high, the resin surface separates immediately from the mold and then transferred again on the surface of the mold during the subsequent interruption step of the movement of the cavity. This is likely to give rise to the problem. of damaging the appearance of the surface of the piece molded

According to the invention, the period of time during which the cavity is kept full of resin immediately after finishing the filling until the beginning of the expansion of the cavity depends on the temperature of the resin poured, the mold temperature, etc., and is preferably from 2 to 20 s, more preferably from 2 to 15 s. If the maintenance time is too long, the layer of skin on the surface on the resin surface becomes thick reducing substantially the thickness of the expanded layer. This entails the probability of that only a low ratio foam body will be available of expansion

The period of time during which the cavity remains full of resin immediately after the end of filled to the beginning of the primary enlargement of the cavity is preferably 0.1 to 11 s, more preferably 0.5 to 5 s. He period of time during which the enlargement of the cavity is interrupts between the primary and secondary expansion steps of the cavity is preferably 0.5 to 30 seconds, more preferably from 3 to 20 s. If the duration of the interruption is too short, the cell film will break like when the amount of primary enlargement of the cavity is large in the step of primary enlargement of the cavity, which entails, in consequently, the probability that the cells join forming older cells. If the duration of the interruption is excessively long, the resin cools, with the possibility that the resin will stretch exceeding the expansion pressure, with the result that the resin will stop expanding to the desired amount of cavity enlargement or develop irregularities surface different from the shape of the mold.

The "secondary expansion speed of the cavity "according to the invention is preferably 0.5 to 15 mm / s, more preferably 5 to 10 mm / s. If the speed is too low, the resin cools during the enlargement of the cavity, with the possibility that the resin is stretched exceeding the pressure of expansion. As a result, the resin stops expanding until the desired increased cavity width or is it likely that develop surface irregularities different from the shape of the mold.

When the speed of the expansion of the cavity is excessively large, the resin surface separates immediately after the mold and transferred back to the surface of the mold when the cavity is taken to its detention in the final position of cavity enlargement. This is likely to give rise to the problem of damaging the appearance of the surface of the molded part.

Figure 1 is a diagram showing a example of injection molding apparatus for use in a procedure to produce a thermoplastic resin body foamed of the invention.

Figure 2 is a horizontal section view which shows a mold before the cavity of the same.

Figure 3 is a horizontal section view which shows the mold of figure 2 after the Cavity of the same.

Figure 4 includes views in horizontal section which shows a mold to produce thermoplastic resin bodies foamed

Figure 5 is a horizontal section view which shows other means of cavity enlargement.

Figure 6 is a horizontal section view which shows an enlarged cavity by the means of expanding cavity shown in figure 4.

Figure 7 is a graph showing the relationship between cavity enlargement speed and time involved in the process to produce the resin body thermoplastic foam.

Figure 8 is a side elevation showing the foam body obtained.

Figure 9 is a diagram to illustrate the forces that take place when a resin body is bent thermoplastic foam.

Figure 10 is a photograph showing in section a foamed thermoplastic resin body obtained in the example 7.

Figure 11 is a photograph showing in section a foamed thermoplastic resin body obtained in the example 8.

Figure 12 is a graph showing the relationship between cavity enlargement speed and time involved in a conventional procedure to produce a body of foamed thermoplastic resin.

Figure 13 includes section views horizontal showing a conventional mold to produce the Foamed thermoplastic resin body.

Embodiments of the present invention are will describe below in detail with reference to drawings.

Figure 1 is a diagram showing an example of an injection molding apparatus. In Fig. 1, the injection molding apparatus is indicated in 1, in 11 a resin plasticizing-kneading cylinder of the apparatus 1, in 12 a pressure resistant chamber disposed above the cylinder 11 and positioned towards the rear end thereof, in 13 a hopper arranged above the chamber 12, and in 14 a cylinder for carbon dioxide for use as a foaming agent. The cylinder is connected to the pressure-resistant chamber 12 by a channel 142. A pressure regulating valve 141 is arranged in the channel 142. Valves are indicated at 121, 122, 123 and 124. An injection molding mold 2 comprises a stationary mold member 21 and a movable mold member
22

A polypropylene (HMS-PP, product of Montell-JPO, 127 ° C at the point of fusion), which serves as a thermoplastic resin, was placed in a hopper 13 and was supplied to chamber 12 with valve 122 open. Then, valves 122, 123, 124 were closed and the introduced carbon dioxide - adjusted to a pressure of 5.5 MPa per pressure regulating valve 141 - in chamber 12 through of valve 121.

The interior of the chamber 12 resistant to pressure was maintained at a carbon dioxide pressure of 5.5 MPa and a temperature of 45 ° C for two hours to dissolve the dioxide Carbon in thermoplastic resin.

Incidentally, an inert gas can dissolve in a high pressure thermoplastic resin dissolving the gas inert in the molten resin or by dissolving the gas in the resin in a solid state. Any one of these methods can be used or The two methods can be used in combination.

The inert gas can dissolve in the resin thermoplastic melted at high pressure, for example by mixing the gas with the resin inside the injection cylinder 11 through a elbow arranged in an intermediate portion of the cylinder. In this case, the molten thermoplastic resin serves as a seal to Pressure.

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The inert gas can dissolve in the resin solid thermoplastic, for example:

(one)

dissolving inert gas beforehand in thermoplastic resin in the form of pills or a powder inside a pressure vessel or similar, or

(2)

dissolving the inert gas in the resin thermoplastic supplying the gas to a region of the apparatus of injection molding from the hopper to a transport portion of solids thereof.

In the case of the above method (2), it is desirable incorporate a pressure resistant sealing structure in the worm drive shaft and hopper in order to prevent inert gas from evaporating from the injection cylinder eleven.

Inert gas can be supplied from the gas bottle 14 directly to the injection cylinder 11 or the gas can be supplied pressurized with a plunger pump not illustrated.

The thermoplastic resin containing dioxide carbon was supplied from the pressure-resistant chamber 12 to the cylinder 11 set at 190º C through valve 124. Resin collected in a measuring portion towards the front end of the cylinder 11 was injected into an initial cavity 3 with a thickness of 3 mm through a gully 5 and a trough 4, as shown in the figure 2.

With reference to figures 2 and 3, the member of mobile mold 22 comprises a moving part 221 that can be moved forward or backward in the direction of the thickness of the cavity, and a wedge piece 222 movable up or down by the operation of a hydraulic cylinder 223 connected to a hydraulic unit 224. The cavity 3 is decreased when the piece of wedge 222 is lowered as seen in figure 2 or enlarged when the wedge piece 222 rises, as shown in the figure 3.

Figure 4 shows an example of the mold of the invention.

With reference to the mold 2a shown in the figure 4, a movable mold member 22a comprises a movable part 221a and a stationary part outside the moving part 221a, an initial cavity 31 is defined by a stationary mold member 21a, the part mobile 221a and the stationary part, and one end of a moving part 221a of the movable mold member 22a can move forward or towards back (51 or 52) inside cavity 31 along the direction of the thickness of the cavity. As shown in Figure 4 (a), the initial cavity 31 is in the form of a tube with a bottom and a lowered section along the direction of movement towards forward or backward. Therefore, when the initial cavity 31 is filled with molten resin as shown in Figure 4 (b), a layer of charged resin 40 is formed which is tubular, has a bottom and a recessed section in the direction of movement towards front or back and comprises a main body portion 41 and a tubular peripheral portion 42. When the moving part 221a then go back to address 52 as shown in Figure 4 (c), the central portion of the resin layer loaded 40 expands following the retraction of the moving part 221a to form a foamed body 4 as desired.

The tubular peripheral portion 42 of the layer of charged resin 40 can be maintained at a high temperature by doing that the thickness t4 of the peripheral portion 42 be greater than the t3 thickness of the main body portion 41. This causes the 4 foam body is easier to produce by expanding the cavity 31.

Figures 5 and 6 are diagrams to illustrate another example of means to expand a cavity 3. Instead of extension means for cavity 3 shown in figures 2 and 3, whose means include wedge piece 222, the hydraulic unit 224 and hydraulic cylinder 223, is used as this means of enlargement an opening device for a mold 2b of a injection molding apparatus 1.

A moving part 221b can be moved towards front or back together with a member mounting plate 15 of mobile mold by the operation of the drive rod 16 of a hydraulic cylinder 17 of the apparatus 1. Figure 4 shows the cavity 3 decreased, with moving part 221b displaced towards front together with mounting plate 15. Figure 5 shows the extended cavity 3, with the moving part 221b displaced backwards together with the mounting plate 15.

Figure 7 shows the relationship between the Cavity enlargement speed and time involved in the process of the invention to produce resin bodies thermoplastic foam. The cavity expands at a speed of V1 in a step of primary cavity enlargement, that is, during the period from the beginning until the moment T1, the extension is interrupts at time T1, and the cavity expands at a speed V2 in a secondary expansion step of the cavity, that is, from moment T2 to moment T3.

Example 1

(First and third features of the invention)

With reference to Figure 4 (a), poured a molten polypropylene resin into the initial cavity 31 in the form of a tube with a bottom and a recessed section along of the direction of movement forward or backward (3 mm width t3 along this direction of the cavity width main 34 corresponding to the bottom portion thereof). TO then, cavity 31 was kept in its loaded form with the resin and moving part 221a moved backwards 12 mm raising the wedge piece 222 with hydraulic cylinder 223 after the average resin temperature at 180, 150 or 120 ° C (2 s, 9 s or 22 s, respectively, of retention time since the end of filling until the cavity is enlarged) in order to extend the cavity 31 to the increased final cavity width. Speed Cavity 31 enlargement at this time was 5 mm / s.

The average temperature of the resin was controlled cast when moving part 221 had to be moved back keeping the initial cavity 31 in its form loaded with the resin for a specified period of time. The temperature of 190ºC for the enlargement of the cavity listed in Table 1 below is the temperature involved in the condition that the cavity is kept in its loaded form with the resin for 0 s.

The foamed body of thermoplastic resin in the cavity 31 was then cooled for 240 s, and then opened the mold 2 to remove the foamed body 4.

Table 1 shows the result obtained observing the foamed bodies thus prepared.

TABLE 1

one

Evaluation

Table 1 reveals that the foamed body of the Example 1 had thin cells in the case where the average temperature of the resin was 120 ° C or 150 ° C when the cavity was enlarged. When the average resin temperature exceeded the range [the point melting + 30 ° C], as in the case of 180 or 190 ° C, were obtained thick cells with large gaps found inside the expanded resin body.

When the average temperature of the resin stops expand the cavity was 150 ° C or 180 ° C, the body exhibited a large smoothness. However, when the average temperature of the resin stops the cavity enlargement was below the previous range, for example 120 ° C, the thermoplastic resin ceased to expand to the desired way and to provide a surface foam body smooth. The resin also stopped expanding to the desired shape and of providing a smooth surface foam body when the average temperature of the resin was 190 ° C for the expansion of The cavity.

Example 2

(Second and fourth characteristics of the invention)

Primary cavity enlargement step

With reference to Figure 4 (a), poured a molten polypropylene resin into the initial cavity 31, which was 3 mm wide t3 of width 34 of the cavity principal. The cavity 31 was then maintained its shape loaded with the resin for 0.5 s, and moving part 221a moved backward (4 mm) to an intermediate position by raising the wedge piece 222 with hydraulic cylinder 223 after the temperature drop  resin average at 185 ° C. The speed of expansion of the cavity 31 was 5 mm / s in this primary expansion step of the cavity.

Secondary cavity enlargement step

The extension of the cavity in the intermediate position, and the moving part 221a is then moved backwards raising the wedge piece again 222 with hydraulic cylinder 223 after the fall of the temperature of the central resin portion in the direction of the thickness at 190ºC, 170ºC, 150ºC or 120ºC (0 s, 10 s, 14 s or 31 s, respectively, of the interruption time of the extension of the cavity) to extend the cavity to a final cavity width increased of 26 mm. The cavity enlargement speed 31 at this time it was 10 mm / s.

The thermoplastic resin body foamed in the cavity 31 was cooled for 360 s after this step of secondary enlargement of the cavity and mold 2 was opened to remove the foamed body 4.

Table 2 shows the result obtained observing the foamed bodies thus prepared.

TABLE 2

2

Evaluation

Table 2 reveals that the foamed body of the Example 2 had thin cells when the average temperature of the resin to begin the primary cavity enlargement step it was 185 ° C, which was within the range of [melting point at melting point + 60 ° C], and when the portion temperature resin core along the thickness direction for initiate the secondary expansion step of the cavity was 170 ° C,  150 ° C or 120 ° C. However, if the cavity enlargement was not interrupted between the primary and secondary expansion steps of the cavity and when the temperature of the central resin portion to along the thickness direction to start the passage of secondary expansion of the cavity was 190 ° C, there was a hollow in the central portion of the thermoplastic resin body Foamed obtained, with thick cells present in the other portion. In addition, the thermoplastic resin foamed body left to expand to the desired way and to provide a body smooth surface foam.

In the case where the serving temperature resin core was 170 ° C or 150 ° C when the secondary enlargement of the cavity, the foamed body had excellent surface smoothness. However, if the temperature of the central portion of resin was below the melting point, for example 120 ° C, when the secondary extension of the cavity, the foamed thermoplastic resin body stopped expand to the desired shape and provide a foamed body smooth surface.

Example 3

The same procedure was performed as in step of primary expansion of the cavity of Example 2, except that in the primary expansion step of the cavity the moving part 221a moved back after the average temperature of the resin poured into the initial cavity will fall to 195, 180 or 125 ° C.

The same procedure was performed as in step of secondary expansion of the cavity of Example 2, except in that in the secondary expansion step of the cavity, interrupted the movement of the cavity until the temperature of the central portion of the resin in the direction of its thickness decreased to 160 ° C.

Table 3 shows the result obtained. observing the foamed bodies prepared.

TABLE 3

3

Evaluation

Table 3 reveals that the foamed body of the Example 3 had thin cells when the average temperature of the resin was 180 ° C or 125 ° C at the time the primary enlargement of the main cavity.

However, in the condition that the average resin temperature exceeded the range of [the point of melting + 60 ° C], for example 195 ° C, when the cavity was enlarged, the Foamed body had thick cells, with a hollow portion found in its central portion.

The foamed body was excellent in smoothness if the average resin temperature was 195 ° C or 180 ° C when performed the primary enlargement of the cavity. However, if the temperature average resin was below the previous range, for example 125 ° C, when the primary enlargement of the cavity was performed, the thermoplastic resin body stopped expanding to form desired and to provide a surface foam body smooth.

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Example 4

The same procedure was performed as in step of primary expansion of the cavity of Example 2, except that in the primary expansion step of the cavity the moving part 221a moved back to expand cavity 31 at a speed of 0.5, 5 or 10 mm after the average resin temperature poured into the initial cavity will fall at 31 to 180 ° C.

The same procedure was performed as in step of secondary expansion of the cavity of Example 2, except in which in the secondary expansion step of the cavity was interrupted the movement of the cavity until the portion temperature center of the resin in the direction of its thickness will fall to 160 ° C.

Table 4 shows the result obtained. observing the foamed bodies prepared.

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TABLE 4

4

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Evaluation

Table 4 reveals that the foamed body of the Example 4 had thin cells when the speed of the enlargement Primary cavity was 5 mm / s. Thick cells were observed if the primary expansion rate of the cavity was out of the range of the invention.

The foamed body had an excellent appearance when the expansion speed of the main cavity  It was 0.5 or 5 mm / s.

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Example 5

The same procedure was performed as in step of primary expansion of the cavity of Example 2, except that in the primary expansion step of the cavity, the moving part 221a moved back after the average temperature of the resin poured into the initial cavity will fall at 31 to 180 ° C.

The same procedure was performed as in step of secondary expansion of the cavity of Example 2, except in which in the secondary expansion step of the cavity was interrupted the movement of the cavity until the portion temperature center of the resin in the direction of its thickness will fall to 160 ° C with cavity 31 enlargement speed set to 1, 10 or 20 mm / s

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Table 5 shows the result obtained observing the foamed bodies prepared.

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TABLE 5

5

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Evaluation

Table 5 reveals that the foamed body of the Example 5 had thin cells when the speed of the enlargement The secondary cavity was 10 mm / s.

Thick cells or hollow portions were observed if the secondary expansion rate of the cavity was 1 or 20 mm / s

The foamed body had an excellent appearance when the secondary enlargement speed of the cavity was 1 or 10 mm / s. In addition, a molded part was obtained expanded of excellent smoothness when the speed of expansion The secondary cavity was 10 or 20 mm / s.

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Example 6

The same procedure as the step of primary cavity enlargement of Example 2, with the exception of pouring, in the primary expansion step of the cavity, a molten thermoplastic resin in main cavity 31 shown in Figure 4 (a), which was 3 mm wide t3 of space 34 of the main cavity in the direction of forward movement or back, 0, 3 or 12 mm wide t4 of the cavity space 32 peripheral, and 0, 5 or 15 mm in length t5 of the cavity space 32 peripheral in the direction of forward or forward movement back, and moving the moving part 221a back after the average temperature of the resin poured into cavity 31 will fall to 180 ° C

The same procedure was performed as in step of secondary expansion of the cavity of Example 2, except in which in the secondary expansion step of the cavity was interrupted the movement of the cavity until the portion temperature center of the resin in the direction of the thickness of the same drop at 160 ° C.

Figure 8 shows the foam body obtained. Table 6 shows the thickness 17 of a left side portion of the foamed body 4, the thickness t2 of the body from the portion of drinker to the lower end of the central portion, and the t8 thickness of a right side portion thereof.

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TABLE 6

6

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Evaluation

With an increase in space length t5 32 of peripheral cavity along the direction of movement forward or backward, the difference between the thickness t2 of the central portion of body 4 and thickness t7, t8 of opposite side portions thereof.

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Example 7

(Characteristics 12 and 13 of the invention)

Primary cavity enlargement step

With reference to Figure 4 (a), a molten polypropylene resin was poured into the initial cavity 31, which was 2 mm wide t3 of the width 34 of the cavity principal. The cavity 31 was then kept in its shape loaded with the resin for 5 s, and the moving part 221a moved back (2 mm) to an intermediate position by lifting the piece wedge 222 with hydraulic cylinder 223. The speed of Cavity 31 enlargement was 15 mm / s in this step of primary enlargement of the cavity.

Secondary cavity enlargement step

The movement of the cavity was interrupted in the intermediate position for 0.5 s and moving part 221a moved to then backwards raising the wedge piece 222 again with the hydraulic cylinder 223 to extend the cavity to a final cavity width increased by 20 mm. The speed of Cavity 31 enlargement at this time was 15 mm / s.

The thermoplastic resin body foamed in the cavity 31 was cooled for 120 s after this step of secondary enlargement of the cavity, and mold 2 was opened to remove the foamed body 4.

Body characteristics were measured Foamed well prepared. Table 7 shows the results.

As is evident from the photograph of a section shown in figure 10 (enlarged to x6 under a microscope), the foamed thermoplastic resin body is composed of a portion b of expanded inner layer and two portions  of surface layer to which they had portion b sandwiched between them and forming a single piece with them.

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Example 1 comparative

(Example with cells big)

A foamed body was prepared therewith procedure as in Example 7, with the exception of maintaining the molten polypropylene resin containing carbon dioxide in the cavity for 2 s after pouring and until the beginning of the primary enlargement of the cavity, and to extend the cavity to a speed of 3 mm / s in the primary expansion step of the cavity.

Table 7 shows the results obtained. measuring the characteristics of the prepared foam body.

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Example 2 comparative

(Example with a small relationship of cells open)

A foamed body was prepared in the same way than in Example 7, with the exception of maintaining the resin of molten polypropylene containing carbon dioxide in the cavity for 2 s after pouring and until the beginning of the primary cavity enlargement, extend the cavity to a speed of 3 mm / s in the primary expansion step of the cavity, interrupt cavity enlargement for 3 s between the steps of primary and secondary cavity enlargement, and expand the cavity at a speed of 10 mm / s in the passage of secondary enlargement of the cavity.

Table 7 shows the results obtained. measuring the characteristics of the prepared foam body.

TABLE 7

7

Example 8

(Characteristics 14th and 15th of the invention)

A foamed body was prepared in the same way than in Example 7, with the exception of maintaining the resin of molten polypropylene containing carbon dioxide in the cavity for 11 s after pouring and until the beginning of the primary cavity enlargement, extend the cavity to a 10 mm / s speed in the primary expansion step of the cavity, interrupt cavity enlargement for 3 s between the steps of primary and secondary cavity enlargement, and move the moving part 221a back to a cavity width increased end of 30 mm in the secondary expansion step of the cavity to extend the cavity 31 at a speed of 5 mm / s .

Table 8 shows the results obtained. measuring the characteristics of the prepared foam body.

As is evident from the photograph of a section shown in figure 11 (enlarged to x4 under a microscope), the foamed thermoplastic resin body obtained it consisted of a portion b of expanded inner layer and two portions a of surface layer with portion b sandwich between them and forming a single piece with them.

Example 3 comparative

(Example with cells big)

A foamed body was prepared in the same way than in Example 7, with the exception of maintaining the resin of molten polypropylene containing carbon dioxide in the cavity for 7 s after pouring and until the beginning of the primary cavity enlargement, extend the cavity to a 10 mm / s speed in the primary expansion step of the cavity, interrupt the enlargement of the cavity for 1 s between the steps of primary and secondary cavity enlargement, and move the moving part 221a back to a cavity width increased end of 17 mm in the secondary expansion step of the cavity to extend the cavity 31 at a speed of 5 mm / s .

Table 8 shows the results obtained. measuring the characteristics of the prepared foam body.

Example 4 comparative

(Example with flatness relationship big)

A foamed body was prepared in the same way than in Example 7, with the exception of maintaining the resin of molten polypropylene containing carbon dioxide in the cavity for 10 s after pouring and until the beginning of the primary cavity enlargement, extend the cavity to a 10 mm / s speed in the primary expansion step of the cavity, interrupt the enlargement of the cavity for 0.5 s between  the steps of primary and secondary cavity enlargement, and move the moving part 221a back to a cavity width increased end of 17 mm in the secondary expansion step of the cavity to extend the cavity 31 at a speed of 5 mm / s .

Table 8 shows the results obtained. measuring the characteristics of the prepared foam body.

TABLE 8

8

The present invention has the following advantages.

Homogeneous foamed bodies can be prepared with thin cells using the production process of thermoplastic resin bodies foamed according to the characteristic first or third of the invention.

Homogeneous foamed bodies can be prepared with a high expansion ratio and variable cell diameters using the resin body production process thermoplastic foam according to the second or fourth characteristic of the invention.

Homogeneous foamed bodies can be prepared With high dimensional accuracy, excellent appearance of smooth surface and fine cells using the procedure of production of foamed thermoplastic resin bodies according to the fifth characteristic of the invention.

Homogeneous foamed bodies can be prepared With high dimensional accuracy, excellent appearance of smooth surface, high expansion ratio and fine cells using the resin body production process thermoplastic foamed according to the sixth characteristic of the invention.

Foamed bodies can be prepared which are make up as desired even in its peripheral portions using the resin body shaping mold thermoplastic foam of the eighth characteristic.

The resin body shaping mold thermoplastic foamed according to the ninth characteristic of the invention is adapted to keep the resin in its portion peripheral at a temperature higher than that of the resin in the piece mobile and therefore to produce good foamed bodies stability that conform as desired even in its portions peripherals Since the movable mold member can move in different times for enlargement by this procedure, it is possible to prepare homogeneous foamed bodies of ratio of high expansion and variable cell diameters.

Industrial applicability

The invention provides foamed bodies of thermoplastic resin that have a high expansion ratio, a desired shape and cells of the desired diameter, especially cells fine The foamed thermoplastic resin bodies provided by the invention they have a compression stiffness and a stiffness to Extremely high flex, light weight and excellent properties thermal insulation.

Claims (9)

1. Procedure for producing a foamed body of a thermoplastic resin by pouring the molten thermoplastic resin and containing a foaming agent into a cavity of a mold and then expanding the cavity to expand the resin, including the procedure the steps of: keeping the cavity in its form filled with the resin for a predetermined period of time after the resin containing the foaming agent is completely poured into the cavity, and extending the cavity to an increased final cavity width after the predetermined period of time, characterized in that extends the cavity to an increased final cavity width after the average temperature of the molten resin within the cavity reaches the range of the melting point of the resin to [melting point + 30 ° C]. 2. Method according to claim 1, characterized in that the expansion process includes: a primary cavity expansion step to a predetermined value less than an increased final cavity after a predetermined period of time following the molten resin, and a step of Secondary cavity enlargement to the increased final cavity width after interrupting the cavity enlargement for a specified period of time. 3. Method according to claim 2, characterized in that the primary expansion step of the cavity is initiated after the average temperature of the molten resin within the cavity reaches the range of the melting point of the resin to [the melting point + 60 ° C], and the secondary expansion step of the cavity begins after the temperature of the resin in its central portion with respect to the thickness thereof reaches a temperature from the melting point to [the melting point + 50 ° C ]. 4. Method according to any of the preceding claims, characterized by extending the cavity at a speed of 2 to 5 mm / s. 5. Method according to claims 2 or 3, characterized in that the cavity is enlarged at a speed of 5 to 10 mm / s in the secondary expansion step of the cavity. Method according to any one of claims 1 to 5, characterized in that the foaming agent is an inert gas. 7. Mold for forming a foamed body of a thermoplastic resin according to the method of any of claims 1 to 6, having a cavity defined by a stationary mold member and a movable mold member, the movable mold member being provided with a movable part (221a) movable forwards or backwards along the direction of the thickness of the cavity, and a stationary part outside the movable part, the movable part being configured to define a space (32) of peripheral cavity by middle of the stationary part, an outer peripheral surface of the movable part and a wall (33) of peripheral cavity, and a space (34) of main cavity by means of a front end face of the moving part and a wall of cavity ( 35) opposite it when the moving part moves forward, characterized in that the width (t4) of the peripheral cavity space (32) is two to four times the width (t3) of the main cavity space (34) to the. A mold according to claim 7, characterized in that the length (t5) of the peripheral cavity space (32) in the forward or backward direction of movement is greater than the width (t3) of the main cavity space (34) in the direction of movement forward or backward. 9. Mold according to claim 8, characterized in that the length (t5) of the peripheral cavity space (32) in the forward or backward direction of movement is 50 to 70% of an increased final cavity width (t6).